1. Field of the Invention
The invention relates to an air pressure regulating device for ink cartridges that can be applied to ink cartridges of ink jet printers, and particularly relates to an air pressure regulating device that uses elastic gastight materials to seal gas vents so that the negative pressure inside the ink cartridge can be maintained within an operating range in which the ink cartridge can operate normally and ink leakage can be prevented from the ink pens.
2. Related Art
Ink jet printers are already one of the most reliable and effective printers nowadays. Conventionally, an ink jet printer possesses a ink pen, which can move above the printed media repeatedly and eject ink droplets from the ink pen on the printed media. The printhead is controlled by a control system to move to a required position and eject ink droplets from the ink pen on the printed media via the printhead so that the ejected ink droplets form the required images or data. These kinds of printers usually possess an ink pen constructed mainly of an ink cartridge functioning as an ink supply source and a printhead.
Two commonly utilized systems that can be applied to command the printhead to eject ink droplets by a sequence of control orders are the thermal bubble system and the piezoelectric system. The printheads for these two systems possess usually more than one orifice and each of the orifices is connected to the associated ink chamber. When the systems are in use, the ink is guided from the ink cartridge into the ink chambers of the printhead and then is ejected through the orifices from the ink chambers on the printed media. For the printhead of the thermal bubble system the ink inside the ink chambers is reheated to vaporize in a very short time by a thin-film resistor and then the ink droplets can be ejected through the orifices of the printhead on the printed media by the outward expansive forces induced by the vaporization of the ink. For the printhead of the piezoelectric system some piezoelectric elements are settled so that a specific quantity of ink inside the ink chambers is ejected from the ink chambers through the orifices of the printhead on the printed media by the pressure waves induced by the actions of the piezoelectric elements actuated by a sequence of control orders.
Although the two designs of the above-described systems are reliable and effective, the leakage of ink still occurs and until now there is no better mechanism for preventing ink from drooping from the orifices when the printhead is in use. If the ink droops from the orifices, then the locations of the ejected ink droplets are not precise and thus the printing quality is negatively influenced. In order to overcome this problem a slight negative pressure must be maintained inside the ink cartridge such that the ink inside the ink cartridge does not droop from the orifices when the printhead is temporarily or continuously not in use.
In the following descriptions the negative pressure is the pressure difference between the ink cartridge and the ambient air under the assumption that the negative pressure inside the ink cartridge is less than that in the ambient air. Enough negative pressure must be maintained inside the ink cartridge so that it can prevent the ink from the orifices of the printhead to droop. But if the negative pressure is too high, then it will counteract the driving forces used to eject the ink droplets from the printhead. The possible influence of this phenomena is that the scales of the ejected ink droplets could not be steadily maintained or could gradually decrease, and the printing quality could become worse.
In order to make the systems operate normally, the negative pressure should be maintained within an operating range, that is, the negative pressure must be high enough to prevent the ink from drooping from the printhead while also low enough so as not to hinder the ejection of ink.
There are already many different technologies that can be utilized to cover the above-discussed requirements for different product specifications. For example, John H. Dion et al., have proposed the invention titled xe2x80x9cMethod and apparatus for extending the environmental operating rage of an ink jet print cartridgexe2x80x9d (U.S. Pat. No. 4,992,802), wherein the negative pressure is controlled by two negative pressure control mechanisms. The first negative pressure control mechanism is utilized to control the flow rates for air pressure regulating or ink-refilling while the second negative pressure control mechanism is applied to control the volume occupied by the ink inside the ink cartridge. By these two negative pressure control mechanisms the negative pressure inside the ink cartridge can be maintained within a normal operating range.
Though with the invention proposed by John. H. Dion the negative pressure inside the ink cartridge can be reasonably controlled, the structures are rather complicated and the volume of the ink cartridge in which ink is stored cannot be optimally utilized. Therefore James E. Pollacek has proposed other design titled xe2x80x9cRegulator for ink-jet pensxe2x80x9d (U.S. Pat. No. 5,040,002) having a simpler structure to the one from John. H. Dion. In this invention a ventilating vent is settled in the ink cartridge and above the ventilating vent a metallic valve and valve seat are also set. This metallic valve can be closed by magnetic forces until the negative pressure inside the ink cartridge is large enough to let the negative pressure of the ambient air reopen the valve so that the ambient air can refill the ink cartridge. After that the magnetic force once again closes the metallic vale so that the ink cartridge is sealed to maintain its internal negative pressure. By the above described mechanism the negative pressure inside the ink cartridge can be kept within a specific operating range.
Although this inventive design for ink cartridges in which the metallic valve is controlled by magnetic force to let the ambient air refill the ink cartridge has a simpler structure, the metallic valve and valve seat are affected strongly by magnetic forces to change their functions so that the specific operating range for the pressure cannot be preciously controlled and consequently the printing quality will seriously decrease if the products with this design are placed near strong magnetic fields.
In light of the invention proposed by James E. Pollacek, the object of the present invention is to design an ink cartridge that is simpler in structure and for which the associated metallic valve and valve seat will not be affected by magnetic forces. In accordance with the design of the invention a ventilating vent is settled in the ink cartridge such that the ink cartridge can be connected through this ventilating vent to the ambient air, and this ventilating vent is also directed to a fixed seat. On the fixed seat a gas vent is settled and directed to the ink cartridge. On the outside region of the gas vent a layer of elastic gastight material is covered so that it can be used to seal the gas vent to keep the ink cartridge sealed under ordinary conditions. When the ink cartridge is in use, the free liquid surface level of the ink inside the ink cartridge gradually decreases during the printing operations, while the volume occupied by the air inside the ink cartridge gradually increases. This is because the ambient air cannot refill the ink cartridge as the gas vent is sealed by the layer of the elastic gastight material. From the Boyle and Charles"" law it is understood that the gas pressure decreases when the gas volume increases if the gas pressure and temperature do not vary. Therefore the pressure inside the ink cartridge steadily increases during continuous printing operations. When the pressure difference between the inside and outside regions of the ink cartridge reaches a critical value, the layer of the elastic gastight material utilized to seal the gas vent is pressed away from the gas vent by the atmospheric pressure so that a small quantity of ambient air can flow into the ink cartridge to return the negative pressure inside the ink cartridge to within a normal operating range. Because the pressure difference between the outside and inside regions of the ink cartridge reduces once more and the force induced by the elasticity of the gastight material is larger than that induced by the atmospheric pressure, the gas vent can once again be sealed such that the negative pressure inside the ink cartridge can be maintained.
Further scope of applicability of the invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.